1. Field of the Invention
This invention relates to a single-wafer-processing type CVD (Chemical Vapor Deposition) apparatus and method for forming a thin film on one wafer at a time. The present invention particularly relates to a CVD apparatus and method using a mechanism for vaporizing a liquid raw material.
2. Description of the Related Art
In recent years, as semiconductor devices become highly integrated, heat-unstable liquid raw materials or solid raw materials with low vapor pressure have become used as reaction materials in addition to conventional high-pressure gas materials or liquid raw materials with relatively high vapor pressure. Simultaneously, as the use of larger-diameter wafers has progressed to improve throughput, an amount of vaporized liquid raw material required for deposition reaction has been increasing.
For example, a vapor pressure of Cu(hfac)tmvs (Hexafluoroacetylacetonatocopper: trimethylvinylsilane adduct), a liquid raw material used for forming Cu interconnect having electrical resistance lower than that of Al, is as low as 0.3 mmHg/43° C. For deposition of a 200 mm-diameter wafer, a vaporized material amount of 1.5 g/min. is sufficient. However, a vaporized material amount of 3.0 g/min. is required for a larger diameter wafer, i.e. a 300 mm-diameter wafer. To obtain this amount, it requires heating a conventional vaporizer at 80° C. Because Cu(hfac)tmvs is heat-unstable, decomposition starts if it is heated at 40° C. or higher, which causes a problem.
Additionally, chlorides or organic metal complexes used as raw materials of Hf (hafnium), Sr (strontium), Ba (barium), etc., usability of which for a high-k film used for high-k gates and capacitance or MRAM, etc. are examined, are solid raw materials. In this case, one method used to bring a solid raw material into a reaction chamber is to feed the solid raw material by a carrier gas after subliming it, and another method is to vaporize by a vaporizer a solution, in which a solid raw material is dissolved in a solvent. The former has a problem in that a feed rate is not stable because a surface area of the solid raw material changes due to its vaporization by heating, etc. The latter has a problem in that the solid raw material clogs inside the vaporizer because vaporization temperatures of the solid raw material and the solvent differ, resulting in that predominantly the solvent vaporizes.
Further, the low vapor pressure material is vaporized by the vaporizer provided outside a reaction device and is brought into the reaction device passing through piping and valves. In the past, there was a need for raising a vaporizer temperature to obtain more an amount of a vaporized raw material than those required in order to prevent liquefaction or solidification caused by pressure loss (decreased conductance) in the piping or the valves. In Japanese Patent No. 3112721, Japanese Patent Laid-open No. 2001-148347, Japanese Patent Laid-open No. 2000-199067, and Japanese Patent Laid-open No. 2001-11634, which are incorporated in this application by reference, techniques of increasing an amount of vaporized liquid raw material by increasing a surface area of the vaporizer are disclosed. Additionally, as a method of vaporizing a solid raw material dissolved in the solvent, a technique of vaporizing the solid raw material by bringing vapor pressures of a solvent and a solid raw material closer by a high-pressure delivery liquid developed by Mayumi Arai of MKS Instruments, Inc. is disclosed in “Keisoku Gijutsu” Vol. 25, No. 12 published by Nippon Industrial Publishing Co., pp. 43-47, which is also incorporated in this application by reference.
These methods have problems in that because a vaporizer alone is used for vaporizing a liquid or a solid raw material, the process is influenced by pressure loss in the piping and the valves leading to a reaction chamber, and a vaporization state is dependent on a heating state of the piping and the valves.
Other raw materials with which the above-mentioned problems occur are: TDEAH (Tetrkis-diethylamid-hafnium), Acac2Ba (Bis-acetylacetonato-barium), DPM2Ba (Bis-dipivaloylmethanato-barium), DPM2Ba:(tetraene)n (Bis-dipivaloylmethanatobarium:Tetraethylenpentamine adduct), DPM3Bi (Tris-dipivaloylmethanato-bismuth), DPM2Cu (Bis-dipivaloylmethanato-copper), (hfacCu)2DMVS (Bis-hexafluoroacetylacetonato-copper:Dimethyldivinylsilane adduct), DPM3Ru (Trisdipivaloylmethanatoruthenium), DPM2Sr (Bisdipivaloylmethanato-strontium), DPM2Sr:(tetraene) (Bisdipivaloylmethanato-strontium:tetraethylenepentamine adduct), Ta[N(CH3)2]5 (Pentadimethylamino-tantalum), PET (Pentaethoxytantalum), TDEAT (Tetrakis-diethylamino-titanium), DPM3Y (Trisdipivaloylmethanato-yttrium), etc.